Vision requires proper information transfer from photoreceptors to retinal ganglion cells (RGCs), the output neurons of the retina. This information is distributed by retinal bipolar cells (BCs) along many anatomically and functionally distinct channels. Because BC channels carry different chromatic and temporal information, the light response of a RGC is shaped by the unique combination of BC input it receives. To date, the circuitry of only a few functionally defined RGC types is known, largely because reconstructions by serial electron microscopy are technically challenging and time consuming. Using state-of-the art imaging approaches and molecular tools to visualize synapses and connectivity, we are able to readily reconstruct these circuits by light microcopy. We will establish, and compare, the connectivity patterns of three functionally distinct BC-RGC circuits in the mouse retina, in order to learn new principles or uncover distinct strategies by which BC input can shape RGC output (Aim 1). We will investigate how loss of neurotransmission (Aim 2), or death of retinal neurons (Aim 3) alters circuitry in the inner retina. Because the effects of activity blockade can vary according to how neurotransmission is perturbed in development or in disease, we will determine how disruption of input and/or output of BCs influence their connectivity with RGCs. We will use novel transgenic mice in which transmission is perturbed in distinct ways, and also mice in which activity is altered in either a few or entire populations of BCs. In Aim 3, we will determine the potential of mature BCs and RGCs to re-connect when cells from one or the other population are ablated. We will do this by using transgenic mice in which the magnitude and timing of cell death can be controlled. These findings will be particularly significant for designing cell-based therapies to restore vision. Together, the discoveries of this project will significantly increase our understanding of the cellular mechanisms that regulate the function, assembly and repair of retinal channels necessary for conveying information from photoreceptors to RGCs.